Almost three years ago, I received a call from a friend about a computer my husband had recently sold him. He asked me to come and view some content he had found – they were images of child abuse. I confronted my husband over the phone. He raced home from work and insisted that he had no idea how the images came to be on his computer.

We called the police together and the computer was removed from the friend's house; we were given an incident number. We consulted a friend who knows about IT, who said the images may have got in via a virus or an illegally downloaded film, or some "legitimate" free pornography, to which my husband was addicted at the time. Then, a few weeks later, I caught my husband masturbating to online porn while our youngest son, who was 14 months old, lay sleeping less than a foot away.

This marked the end of our marriage – he moved out that day. In the last three years, I have been plagued with doubts about the computer and my ex's behaviour around our sons. He regularly allows them to sleep in his bed (they are seven and four now) and shares baths with them when they stay with him.

The boys are happy, excelling at school and have plenty of friends, yet I worry. We were told by the police that there was a backlog of devices to be analysed and that we should wait for them to contact us. After 18 months, I rang, explained again and voiced the same concerns I have now.

If those images were indeed put there by mistake, my concerns are unfounded and I'm allowing paranoia to take over. To that end, if I involve social services, I'm essentially ruining a good father's life based on an assumption. If he downloaded the images, I've allowed my children to live with a dangerous man. But I have no proof. G, via email

Your letter worries me greatly. Although I have had to edit it, I referred the full (anonymous) version to the police and the NSPCC. I think you have a gut instinct but are afraid to act on it unless you have proof. Only proper and specialist analysis of your husband's laptop (was he the only previous owner?) will ascertain if the images were downloaded intentionally; so it is imperative that you chase the police up on this. Ring the police back, ask for the head of the department that deals with child protection, give him or her the crime number and explain that you want to know what's happening.

Having child abuse images on a computer is a crime, and while computer analysis takes time, it shouldn't take three years. I'm surprised, given the potential seriousness, that the police haven't already referred it to family services: under Section 47 of the Children Act, potential child protection issues should be investigated by the police and social (family) services. If you are unhappy with the reply, then you need to make a complaint at ipcc.gov.uk.

At the same time, please ring the NSPCC helpline (0808 800 5000) and the Stop it Now helpline (0808 1000 900). You can talk to a trained person who will listen, explain what might happen next and advise on what to say to your children to best protect them. I would also strongly advise you to contact family services (find yours at direct.gov.uk). At the very least they should come and talk to you and assess whether your children may be in danger. One outcome might be that your husband will only be allowed supervised visits to his sons.

This must be extremely difficult for you, and so many thoughts must be going round your head. Perhaps you have tried to tell yourself that even if your husband did download these images, he wouldn't abuse his own sons or any other child. He might not, but is this a risk you want to take? While no one wants to "ruin a good father's life", your first priority is to your children. You have had this worry for three years, and it hasn't gone away. You are worried about his behaviour around your sons. Please act now.